The present invention relates to ink jet inks. More particularly, the present invention relates to ink jet inks containing co-solvents.
The ink jet method of printing is a rapidly growing, commercially important printing process because of its ability to produce economical, high quality, multi-colored prints. In fact, ink jet print methodology is becoming the print method of choice for producing colored hard copy of computer generated images consisting of graphics and fonts in both narrow and wide format. Ink jet printing is a non-impact and non-contact printing method in which an electronic signal controls and directs droplets or a stream of ink that can be deposited on a wide variety of substrates. Current ink jet printing technology involves forcing the ink drops through small nozzles by piezoelectric pressure, thermal ejection, or oscillation, and onto the surface of a material/media. Ink jet printing is extremely versatile in terms of the variety of substrate material that can be treated, as well as the print quality and the speed of operation that can be achieved. In addition, ink jet printing is digitally controllable.
For these reasons, ink jet printing methodology has been widely adopted for industrial marking and labeling. In addition, ink jet printing methodology has also found widespread use in architectural and engineering design applications, medical imaging, office printing (of both text and graphics), geographical imaging systems (e.g., for seismic data analysis and mapping), signage, in display graphics (e.g., photographic reproduction, business and courtroom graphics, graphic arts), and the like. Finally, ink jet printing has now also been used to create an image on a variety of textile substrates such as cotton, silk and synthetic materials.
Both dyes and pigments have been used as colorants for such ink jet ink formulations. When dyes are used in ink jet inks (usually in the form of dye solutions), they rarely exceed concentrations of 4 weight percent (that is percent total dye solids) of the mass of the ink. In the case of water-based ink jet inks intended for textile applications, it is often desirable to increase the concentration of the dye solids to above 4 percent of the mass of the ink to obtain a deeply colored print on fabrics. In some cases, solid dye concentration may exceed 10 percent of the ink mass. At this level of solid dye concentration, it has proven a challenge to incorporate large amounts of dye into ink jet inks while maintaining good ink jetting properties and useful ink shelf life. In particular, ejection of ink with high levels of dye leads to ink jet blockage and relatively low/short shelf lives as a result of particulate buildup/precipitate in the ink. Ideally, such inks should have shelf lives of at least between 9 and 24 months for the ink manufacture to be practical. Ink jet blockage may be reflected in delayed ink jetting from the ink jet printer. For the purposes of this application, the term xe2x80x9cjettingxe2x80x9d shall refer to the expulsion of ink from an ink jet printer head.
Although several compounds can be used as co-solvents, or additives in ink jet inks, to allow high dye loading with certain dyes, the printing and ink stability is often affected. For instance, the printed image may include breaks, or the image color intensity may be reduced, as seen through visual observation. For the purposes of this application, the term xe2x80x9chigh dye loadingxe2x80x9d shall refer to an ink containing a dye content in excess of about 4 percent of the ink mass, that is a dye solids content in excess of about 4 percent of the ink mass.
In addition to preventing jetting problems, it is particularly advantageous if materials contained in the ink cause the image produced on a particular substrate to be visually brilliant (bright). Materials may cause brightening of a dye by several mechanisms, including but not limited to causing the substrate to swell, thus allowing improved penetration of colorants into the substrate. An alternate possible mechanism for improving the color of a printed image of the substrate may involve preventing the individual dye molecules from associating with one another in the ink to form microscopic aggregates. It is well known that as dye molecules associate to form aggregates, the resulting color becomes duller. Thus, it is seen that in addition to preventing jetting problems through cosolvents, there is a need for certain cosolvents which also impart other advantages to the ink with respect to the color of the ink when printed on to the substrate.
It is therefore seen that there is a need for ink jet inks which allow for high dye loading without sacrificing print quality, ink jetting operations, print color brightness, or shelf life. There is also a need for methods of ink jet printing using ink jet ink with high dye loading capability. In particular, there is a need for methods of ink jet printing textiles, using ink jet ink with high dye content (loading). It is to such needs that the present invention is directed.
A water-based ink jet ink in accordance with one embodiment of the invention includes an N-methylmorpholine-N-oxide (NMMO) co-solvent that allows large amounts of dye (solid dye content in the ink of 4 to 20 percent) to be used in the ink, without compromising ink jetting properties, and while maintaining the stability of the ink for a longer shelf life, and while producing prints with visually brighter color. It should be appreciated that the water-based ink with co-solvent of the present invention can be used with a solid dye content in the ink of less than 4 percent by weight as well. The invention also relates to methods of ink jet printing using ink jet ink with NMMO co-solvent and high dye content of greater than about 4 percent by weight. Desirably, the invention relates to methods of ink jet printing textiles using water-based ink jet ink with NMMO co-solvent and a dye content of greater than about 4 percent. The ink is desirably a reactive, direct, basic, or acid dye- based ink. Furthermore, such formulations, may include at least one additional co-solvent such as an N-methyl acetamide, N-methyl pyrrolidone or tetramethylene sulfone. When included at levels of 0.5-20 percent by weight in a reactive or acid dye-based ink, NMMO allows dye loading to be increased to about 10 percent or more of total dye solids in the ink jet ink, and gives rise to advantageous improvements in the visual appearance of prints when compared to other cosolvents that may be used.